Conventionally, there is a fixing device including a fixing roller, a pressure roller and a heater (see JP 8-54798 A). The fixing roller is heated by the heater. The fixing roller and the pressure roller heat and pressure a recording sheet to fix toner on the sheet. The pressure roller has a core metal, a sponge layer, an elastic layer and a PFA (tetrafluoroethylene perfluoroalkoxy vinyl ether copolymer) tube in this order from radially inside to outside.
However, in this conventional fixing device, since the pressure roller has a core metal, a sponge layer, an elastic layer and a PFA tube in this order from inside to outside, it is difficult for the pressure roller to transport heat which has been transferred directly from the fixing roller to the pressure roller. As a result, it has been the case that temperature of the pressure roller in its axial direction cannot be equalized.
As a consequence, temperature of non-pass areas in continued feeding of small-size recording sheets is increased, causing larger temperature differences between the pass area and the non-pass areas. This involves a need for lowering the heating temperature of the heater to lower the temperature of the non-pass areas, posing a problem of degradation in image quality (fixability) of small-size recording sheets. Furthermore, because of such temperature increases in the non-pass areas, there has been a problem of thermal deterioration of the fixing roller and the pressure roller.